Ellipsometry is a well known approach to determining physical and optical properties of samples. To obtain accurate results, however, requires that values for certain adjustable parameters, including the distance between the ellipsometer and the sample under investigation, (eg. the “height” of the sample), and the angle-of-incidence and plane-of-incidence of the ellipsometer beam with respect to the sample, be known. Where single point on a sample is to be investigated, alignment procedures are well established which provide the required values within acceptable time constraints, (eg. many seconds to a minute or so). However, in situations wherein many points on a large sample, (eg. a mapping of the sample is to be performed), the time required to do conventional alignments at each of the many point investigated can introduce unacceptable, (eg. 5 seconds each), time delays in achieving desired results. The present invention provides an alignment system, and method of its use, which enables very fast, (eg. on the order a second or two), setting of sample height, and angle, and plane-of-incidence, at each spot on the sample to be investigated. The present invention also discloses a relevant sample mapping system which applies the alignment system.
As further insight, it is noted that Pending patent application Ser. No. 11/890,391 Filed Aug. 5, 2007 provides priority back to application Ser. No. 11/105,852, Filed Apr. 14, 2005, with Priority back to Apr. 23, 2004 via Provisional Application Ser. No. 60/564,747, and describes a substantially self contained flying ellipsometer, polarimeter, reflectometer or spectrophotometer system that provides for moving a combined source and detector of electromagnetic radiation over the a surface of a sample in two, (eg. “X” and “Y”), orthogonal dimensions to enable positioning it at desired locations on, and offset distance from sample in a “Z” dimension corresponding to a distance between said combined source and detector and said sample, and which enables easy sequential setting of different Angles-of-Incidence of a beam of electromagnetic radiation to a surface of said sample.
As related in the 391 Pending Application, Ellipsometer Systems generally include a source of a beam of electromagnetic radiation, a Polarizer, which serves to impose a known, (typically linear), state of polarization on a beam of electromagnetic radiation, a Stage for supporting a sample, and an Analyzer which serves to select a polarization state in a beam of electromagnetic radiation after it has interacted with a material system, and pass it to a Detector System for analysis therein. As well, one or more Compensator(s) can be present and serve to affect a phase retardance between orthogonal components of a polarized beam of electromagnetic radiation. A number of types of ellipsometer systems exist, such as those which include rotating elements and those which include modulation elements. Those including rotating elements include Rotating Polarizer (RP), Rotating Analyzer (RA) and Rotating Compensator (RC). A preferred embodiment is a Rotating Compensator Ellipsometer System because they do not demonstrate “Dead-Spots” where obtaining ellipsometric data is difficult. They can read PSI and DELTA of a Material System over a full Range of Degrees with the only limitation being that if PSI becomes essentially zero (0.0), one can't then determine DELTA as there is not sufficient PSI Polar Vector Length to form the angle between the PSI Vector and an “X” axis. In comparison, Rotating Analyzer and Rotating Polarizer Ellipsometers have “Dead Spots” at DELTA's near 0.0 or 180 Degrees and Modulation Element Ellipsometers also have a “Dead Spot” at PSI near 45 Degrees). The utility of Rotating Compensator Ellipsometer Systems should then be apparent. Another benefit provided by Rotating Compensator Ellipsometer Systems is that the Polarizer (P) and Analyzer (A) positions are fixed, and that provides benefit in that polarization state sensitivity to input and output optics during data acquisition is essentially non-existent. This enables relatively easy use of optic fibers, mirrors, lenses etc. for input/output.
Typical construction of spectrophotometer, reflectometer, polarimeter, ellipsometer and the like systems, (eg. Rotating Analyzer, Rotating Polarizer, Rotating Compensator, Modulator Element Ellipsometer), provides a Sample Supporting Stage which is substantially fixed in location. Functionally oriented with respect thereto are a Substantially Fixed Position Source Means (S) for providing a beam of electromagnetic radiation at an oblique angle to said Sample Supporting Stage, and a Substantially Fixed Position Data Detector Means (D) for intercepting Electromagnetic Radiation which Reflects (or Transmits through), a Sample placed on said Sample Supporting Stage. Typical procedure is to place a Sample onto the Sample Supporting Stage, cause a beam of Electromagnetic Radiation to impinge thereonto, and record data produced by the Data Detector Means in response to electromagnetic radiation which enters thereinto, which data is analyzed to provide insight into Sample Optical and Physical properties. Said procedure can include adjustment of the Sample Supporting Stage, or the source and detector of electromagnetic radiation in an “X”-“Y” Plane, and along a “Z” direction perpendicular to its surface, (ie. a vertical position adjustment where the Electromagnetic Radiation approaches the Sample at an oblique angle from a laterally located Source). This purpose of said “Z” adjustment is, for instance, to enable the directing of a beam of Electromagnetic Radiation Reflected from a Sample placed on said Sample Supporting Stage into the Data Detector without moving the Data Detector so it intercepts a beam exiting said Sample. It should be appreciated then that conventional Reflectometer, Ellipsometer and Polarimeter Systems which include provision for such Sample positioning adjustment and orientation with respect to an impinging Electromagnetic beam, typically do so by allowing the Sample Supporting Stage position to be adjusted, rather than by effecting simultaneous change in location of the Source and Data Detector with respect to the Sample Supporting Stage, because it is far simpler to implement Sample Supporting Stage location change. However, an alternative is mount a Reflectometer, Spectrophotometer, Ellipsometer, Polarimeter or the like System to a means for moving it in an “X”-“Y” Plane, and along a “Z” direction perpendicular to its surface of the Sample with respect to a substantially fixed position Stage for supporting a Sample. In either case, however, a relative motion occurs between the Reflectometer, Ellipsometer, Polarimeter or the like System and a sample.
The present invention then breaks with conventional practice by, while typically providing a substantially fixed position Stage for supporting a Sample, providing a Reflectometer, Spectrophotometer, Ellipsometer, Polarimeter or the like System which is mounted to a positioning system which allows adjustment its location in an “X”-“Y” Plane, and along a “Z” direction perpendicular to its surface of the Sample. The present invention then, allows investigation of a large Sample at many locations thereof.
Continuing, while present invention systems can be applied in any material system investigation system such as Polarimeter, Reflectometer, Spectrophotometer and the like Systems, an important application is in Ellipsometer Systems, whether monochromatic or spectroscopic. It should therefore be understood that Ellipsometry involves acquisition of sample system characterizing data at single or multiple Wavelengths, and at one or more Angle(s)-of-Incidence (AOI) of a Beam of Electromagnetic Radiation to a surface of the sample system.
A typical goal in ellipsometry is to obtain, for each wavelength in, and angle of incidence of said beam of electromagnetic radiation caused to interact with a sample system, sample system characterizing PSI and DELTA values, (where PSI is related to a change in a ratio of magnitudes of orthogonal components rp/rs in said beam of electromagnetic radiation, and wherein DELTA is related to a phase shift entered between said orthogonal components rp and rs, caused by interaction with said sample system:TAN(ψ)e(iΔ)=rp/rs While Data taken at one (AOI) and one or multiple wavelengths is often sufficient to allow ellipsometric characterization of a sample system, the results of Ellipsometric Investigation can be greatly enhanced by using multiple (AOI's) to obtain additional data sets. However, while it is relatively easy to provide Wavelength change without extensive difficult physical Ellipsometer System Orientation change, it is typically difficult to change the Angle-of-Incidence (AOI) that a Beam of Electromagnetic Radiation makes to a surface of a sample system. An (AOI) change requires that both the Source of the Electromagnetic Beam and the Detector must be re-positioned and aligned, and such is tedious and time consuming. The present invention therefore can provide means to easily effect (AOI) change. It is also noted that ellipsometric data is typically analyzed by proposing a mathematical model for the sample and regressing it on to said ellipsometric data to arrive at values for parameters in the mathematical model which meet, for instance, a best fit based on a least square error criteria. Further, it is known to obtain data from multiple similar samples and simultaneously regress the similar models onto the different ellipsometric data sets. This technique can break correlation between thickness and refractive index, where the samples have different thicknesses. A similar approach can be applied to data acquired from multiple spots on a single sample.
A Patent to Finarov, U.S. Pat. No. 5,764,365 is disclosed as it describes a system for moving an ellipsometer beam over a large two-dimensional area on the surface of a sample system, which system utilizes beam deflectors.
A Patent to Berger et al., U.S. Pat. No. 5,343,293 describes an Ellipsometer which comprises prisms to direct an electromagnetic beam onto a sample system.
A Patent to Canino, U.S. Pat. No. 4,672,196 describes a system which allows rotating a sample system to control the angle of incidence of a beam of electromagnetic radiation thereonto. Multiple detectors are present to receive the resulting reflected beams.
A Patent to Bjork et al., U.S. Pat. No. 4,647,207 describes an ellipsometer system in which reflecting elements are moved into the path of a beam of electromagnetic radiation.
U.S. Pat. No. 6,081,334 to Grimbergen et al. describes a system for detecting semiconductor end point etching including a means for scanning a beam across the surface of a substrate.
A Patent to Ray, U.S. Pat. No. 5,410,409 describes a system for scanning a laser beam across a sample surface.
U.S. Pat. No. 3,874,797 to Kasai describes means for directing a beam of electromagnetic radiation onto the surface of a sample using totally internally reflecting prisms.
U.S. Pat. No. 5,412,473 to Rosencwaig et al., describes a ellipsometer system which simultaneously provides an electromagnetic beam at a sample surface at numerous angles of incidence thereto.
A Patent to Chen et al., U.S. Pat. No. 5,581,350 is identified as it describes the application of regression in calibration of ellipsometer systems.
A Search of Patents which contain both “ellipsometer” and “Mapping” provided Patents Nos.:                RE40,225 to Finarov;        RE38,153 to Finarov;        U.S. Pat. No. 6,678,043 to Vurens;        U.S. Pat. No. 7,099,010 to Schulz;        U.S. Pat. No. 7,295,330 to Chow;        U.S. Pat. No. 7,327,444 to Naka et al.        
An article by Johs, titled “Regression Calibration Method For Rotating Element Ellipsometers”, which appeared in Thin Film Solids, Vol. 234 in 1993 is also identified as it predates the Chen et al. Patent and describes an essentially similar approach to ellipsometer calibration.
Even in view of the prior art, need remains for:                an ellipsometer system which enables very fast, (eg. on the order a second or two), setting of sample height, and angle, and plane-of-incidence, at each spot on the sample to be investigated and a sample mapping system which applies the alignment system; and        an ellipsometer system which is functionally mounted in a three dimension location means for positioning said selected system at points in a three dimensional setting, including rotational capability.        